Development of Chrome-free Tanning in Supercritical CO2 Fluid using Zr-Al-Ti Complex

Abstract

In the current study, a green technology for the leather tanningprocess was developed, based on Zr-Al-Ti complex as a tanningagent in supercritical CO2 fluid (SCF-CO2). The operatingparameters in the tanning process, including dosage of thetanning agent, reaction time, tanning temperature and tanningpressure, were optimized using the orthogonal testing method.The physicochemical properties, morphological features,organoleptic properties, hydrothermal stability and microscopicfibrous construction of the Zr-Al-Ti tanned leather were alsoevaluated. The results showed that the optimum processconditions were: a tanning agent dosage of 40% of the bated peltweight, a tanning time of 1.5h, a final temperature of 40°C and areaction pressure of 8.5 MPa. The shrinkage temperature, tearstrength, tensile strength and elongation at break of Zr-Al-Titanned leather in water media and in SCF-CO2 exhibited nostatistically significant differences. However, SEM andhistological observations revealed that the fiber bundles ofleather tanned using the Zr-Al-Ti complex tanning agent inSCF-CO2 seemed to disperse more unevenly compared to thosein water media, as well as conventional chrome tanned leather.Moreover, the degree of “opening up” of the fiber bundles andthe visible interspace among them in the Zr-Al-Ti tanned leatherin SCF-CO2 seemed to be much larger. Based on these results, weinfer that the chrome-free tanning process in SCF-CO2 mayendow similar leather characteristics compared to Zr-Al-Titanned leather in a water medium, which could effectivelyreduce the discharge of waste water compared to a conventionalchrome tanning process, thus contributing to the developmentof a greener, or cleaner, technology for the leather tanningprocess.